1. Field of the Invention
The present invention generally relates to a fluid sensor for measuring the flow of a gaseous media, and relates more particularly to a universal flow sensor that is suitable for use in pneumatic circuits exhibiting a wide range of flow rates without substantial modification.
2. Description of the Prior Art
There are essentially three prevailing methods used to measure flow. The first is inferential flow measurement, which senses a difference in pressure across an orifice restriction. The second method uses a thermal sensor, which is also referred to as a constant temperature anemometer, to monitor temperature changes that are dependant upon the speed of the media, as described in U.S. Pat. No. 6,470,741 to Fathollahzadeh, which is incorporated herein by reference. The third method utilizes displacement sensors that detect mechanical displacement of a portion of the sensor caused by the flow of media.
Each of these methods has different application ranges, as well as inherent advantages and disadvantages. Inferential flow measurement generally requires two pressure sensors and a restriction in flow. A temperature sensor is also typically required with this method to compensate for variations in pressure due solely to temperature fluctuations. However, the requirement of multiple sensors substantially increases failure rate and installation cost. Thus, application of inferential flow measurement principles become practical in only limited circumstances.
The remaining two sensor methods do not require multiple sensors, but have other drawbacks. Typically, thermal sensors are used for lower flow rates while displacement sensors are used for relatively higher flow rates. Selection of the most appropriate flow sensor for a particular application requires a detailed knowledge of the anticipated range of measurements, the potential physical characteristics of the media, such as pressure, temperature, and the like, and the environmental characteristics of the location in which the media is to be measured. Accordingly, use of either thermal sensors or displacement sensors generally requires a customized solution for each particular application.
It is an object of the present invention to provide a universal flow sensor and system that are generically applicable and that do not require substantial modification over a wide range of measurement parameters.
It is another object of the present invention to provide a universal flow sensor and system that utilize both thermal sensing and displacement sensing to measure flow over an extended range of physical conditions.
It is yet another object of the present invention to provide a universal flow sensor and system that are able to multiplex flow rate measurement information obtained in a low flow mode with those obtained in a high flow mode.
A flow sensor formed in accordance with one form of the present invention, which incorporates some of the preferred features, includes a mounting plate, bending plate, and sensing assembly. The mounting plate is adapted to be mounted to an internal surface of a conduit, which directs the flow of a gaseous medium. The bending plate is flexibly coupled to the mounting plate and is displaced in response to the flow of gas in the conduit.
The sensing assembly is positioned on the bending plate and includes at least one sensor adapted for sensing temperature changes in response to the flow of gas during a thermal mode. The sensing assembly includes at least one sensor adapted for sensing displacement of the bending plate in response to the flow of gas during a displacement mode. The temperature outputs a thermal mode signal representative of a change in temperature in response to the flow of gas. The displacement sensor outputs a displacement mode signal representative of a change in mechanical stress in response to displacement of the bending plate due to the flow of gas.
A flow sensing system formed in accordance with the present invention, which incorporates some of the preferred features, includes the flow sensor described above, a processor, memory, and a computer. The processor is responsive to the thermal and displacement mode signals and the memory is operatively coupled to the processor. The computer is operatively coupled to the processor and controls calibration of the flow sensor in both the thermal and displacement modes.
These and other objects, features, and advantages of this invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.